Zirconium-treated iron-chromium alloy



Patented Oct. 30,- 1928.

UNITED STATES PATENT OFFICE.

rnnnnmcx m. nncxm', on NEW YORK, N. Y., ASSIGNOR 'ro ELnc'rno METALLURGICAL 'poMPANY, A oonronarron or WEST ,VIRGINIA.

ZIRCONIUM-TREATED IRON -CHBOMIUM ALLOY.

1T0. Drawing. Application filed May 8,

This invention relates to iron-chromium alloys, and comprises a method of treating such alloys whereby a marked improvement is eflected in certain of their physical proper- 5 ties, and their manufacture in a state of uniform excellence is rendered easier. I accomplish this by treating these alloys with zirconium, alone or in combination with certain other elements and notably with silicon. My

invention includes the zirconium-treated a loys resulting from the practice of this method. Zirconium has heretofore been added to Various carbon and alloy steels, as well as to certain non-ferrous metals and alloys, both as a scavenging agent and as an alloying addition. The effect of such addition has varied according to the material treated: for example in the case of plain carbon steels, a marked beneficial action has been noted,

especially under certain conditions of heattreatment; with certain alloy steels on the other hand, and particularly in. the case of the so-called vanadium steels, not only has no material beneficial effect been found, but the use of zirconium has in some cases at least proven to be actually detrimental.

The researches which constitute the basis of the present invention have been directed to the action of zirconium upon ironchromium 'alloys includin the so-called chromium steels, containing irom-about 10% to 60% or upward of chromium, the balance principally iron. These researches have shown, contrary to the results with vanadium steels as mentioned above, that by a proper use of zirconium it is possible not only to improve the soundness of the metal and its freedom from gas and harmful impurities,

40 but also its workin qualities, ductility and toughness, and tens e strength.

It was long the opinion among steel users that chromium steels were inherently more brittle than plain carbon steels, or indeed other alloy steels of like carbon or alloy con-. tent. Later results showed however that this brittleness was due, in most instances at least, to imperfect manufacturing methods rather than to any quality inhering in the alloys 1926. Serial Ito. 107,796.

themselves; but the necessity for special care and precaution in the melting and casting of chromium steels to avoid contal'nination of the metal by oxids, gases or other deleterious substances was emphasized. Such precaut ons are also necessary when zirconium additions are employed if the best grades of metal are to be produced; but it is a highly advantageous property of zirconium that it can, in some measure, correct the defects which might otherwise develop as a consequence of 1mproper or imperfect manufacturing methods.

Certain specific illustrative examples will now be cited, it being clearly imderstood how-. ever that my invention is not limited to the particular compositions of alloys therein mentioned:

Zirconium in the form of a zirconium-silicon alloywas added to an iron-chromium a1- loy containing 7 Per cent. CI G 0.51 Mn 0. 25 Si 0.18

in such proportion that the product contained 0.013 Zr. This alloy was readily rolled into thin sheet and exhibited unusual ductility for an alloy of such high chromium content.

I have also treated alloys much lower in chromium than that mentioned above, asfor .example, alloys in the range known commer- Per cent.

Gr 20.72 0.; 1.13 Si 0. as

The zirconium in this case also was added as an alloy of silicon and zirconium. As an example of chrome-iron which contained zirconium and which was subsequently given a vmost drastic manufacturing test, namely,

the process of making seamless tubing, I mention a heat which analyzed as follows:

Per cent.

C O. 18 Mn 0.96 Si 0. 37 Zr 0.008

70 %0 %Mn %Sl %CI1 %Z! Alloys of essentially similar composition, but without zirconium, could not be hotworked under industrial conditions.

, Zirconium when added to the chrome-iron alloys, increases their ductility and toughness without the sacrifice of strength. As an example, I have treated chrome-iron alloys and subsequently hot worked them to suitable form for machining into test pieces.

' The analysis of the metal tested was as follows % O1 O Mn Si Zr A 25. 58 0. 22 0. 69 0. 56 0. 02 B 25. 41 0. l8 0. 60 0. 58 None added The heat to whichzirconium was added showed an increase of 8.50% in yield point, 5.25%,in maximum strength and 7.00% in reduction of area over the heat without the zirconium addition. Moreover, the standard Izod test values v(a measure of relative toughness or resistance to shock) showed an increase of 50.70% in the zirconium-treated alloy over that without zirconium.

A still further advantage of zirconium treatment is found in the improvement of cold working qualities, as measured by the ductility displayed in the Erichsen tests. A heat which contained zirconium gave Erichsen values 29.6% higher than an alloy of similar analysis but without zirconium treatment. I have also investigated a chrome-iron heat containing Percent. Cr 26.93 c. 19 S1- 35 Mn .59

Part of the metal was treated with ferrosilicon and another part was treated with zirconium silicon, proportioned to give the same silicon content; after which the metal was rolled into 20 gage sheet. Identical heat treatments were used on all samples. The metal treated with zirconium gave an Erichsen value 57.00% greater than the sample Without the zirconium treatment.

In addition to the above alloys, embracing the higher chromium range of workability, I have also investigated the chromium range known to the trade as rustless iron and have obtained data which clearly indicate the beneficial action of zirconium. For example, I have found that a rustless iron of the analysis:

Per cent. Cr 12. 37 O i 06 Si .25 M11 --1 --I 7 treated with zirconium exhibits a tensile strength which is 22.00% greater than a rustless iron of similar composition, namely:

but which was not treated with zirconium, while the ductility is'practically the same.

Impact results for the zirconium-treated alloy were more than double the values obtained for the alloy not treated with zirconium. These results were obtained with the respectivealloys in the annealed condition. Tensile results for the zirconium-treated material, after the alloy had been quenched and drawn, were 35.00% greater than those obtained'for the untreated alloy.

The zirconium may be added in the form of metal, or alloyed with iron or other element not objectionable in the particular composition in question. Zirconium carbide or zirconium compositions high in carbon are to beavoided on account of the insolubility of zirconium carbide in metal baths. Zirconium-silicon is characteristically low in carbon, is freely soluble in the molten alloys, and is advantageously used when the small amount of added silicon is not objectionable. I prefer to add zirconium in such amount that a small percentage of the metal is found in the product, such percentage varying from a few hundredths to four or five tenths of one percent, as illustrated by the above examples. My invention is not however limited toithe use of zirconium insuch proportions. Y

I claim:

1. A wrought article composed of a ferrous alloy containing zirconium and between 10% and 60% of chromium, said alloy having working properties superior to those of an alloy free from zirconium but otherwise identical in composition.

2. A low-carbon steel containing 9 to 30% chromium, less than 3% silicon, and a frac' tion of one'percent of zirconium, and characterized by deep-drawing'properties, superior to those of a steel of identical composition, but without a zirconium content.

4 3. A rolled or forged steel product con- 0 taining 8 to 30% chromium, less than 3% silicon, and a fraction of one percent of zirconium, characterized by deep-drawing properties, superior to those of a product of identical composition, but Without a zirconium content.

In testimony whereof, I afiix mv signature.

FREDERICK B'EcKET'. 

